1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to an injection molding machine equipped with an ejection device and a releasable connection between the ejector drive of the die closing unit and the ejector plates and ejector pins of interchangeable injection molding die assemblies.
2. Description of the Prior Art
When an injection molding machines is used for relatively short production runs, the changeover to the next production run represents a crucial time element in the productive efficiency of the machine. A major component of the changeover time is the time which is required for the exchange of injection molding dies, i.e. the removal of one die assembly and the insertion, connection and conditioning of the next die assembly.
Among the mechanical connections which have to be made in the process of installing a new die assembly is the ejector drive connection which establishes a drive link between the piston rod of the hydraulic actuator of the die closing unit and an axially movable ejector plate with a plurality of ejector rods forming part of each die assembly.
The opening and closing of this drive connection is in many cases made difficult by the additional problem of poor accessibility, particularly in the case of a die closing unit which uses a single axially aligned hydraulic cylinder assembly with a power piston attached to the movable die carrier member, and where the ejector cylinder is arranged inside the power piston. The ejector plate being located at the back side of the movable die half, access to the connection is severely limited.
It has therefore already been suggested previously to arrange the ejector drive in such a way that the drive connection is established automatically by an ejector clutch, in a forward movement of the ejector piston rod in the direction of the ejector plate.
In one prior art device, which is disclosed in U.S. Pat. No. 3,844,703, the ejector clutch is arranged to open every time the ejector piston reaches its rearward end position, the clutch closing again as soon as the ejector piston moves forwardly. This is accomplished by means of a spring-loaded sleeve on the ejector clutch which, by being stopped against an abutment shortly before the end of the ejector return stroke, is displaced relative to the clutch, thereby allowing two radially movable coupling members to free the ejector piston rod.
Apart from the fact that the release and reengagement of the clutch mechanism at the end of every injection cycle inevitably produces wear, with the attendant risk of malfunction, this mechanism has the shortcoming of requiring a considerable amount of space, especially in the axial direction. This may make it difficult to accommodate the clutch mechanism within the movable die half.
In another prior art device, the forward extremity of the ejector piston rod snaps into an ejector clutch, when the ejector piston is moved forwardly against the ejector plate of the movable die half. Release of the clutch requires the use of a rod-like special tool which reaches radially through the attachment plate of the movable die half. This device is disclosed in the German Offenlegungsschrift No. 31 00 659.